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added clojure source goodness
author Robert McIntyre <rlm@mit.edu>
date Sat, 21 Aug 2010 06:25:44 -0400
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9:35cf337adfcf 10:ef7dbbd6452c
1 ;;; fcase.clj -- simple variants of "case" for Clojure
2
3 ;; by Stuart Sierra, http://stuartsierra.com/
4 ;; April 7, 2008
5
6 ;; Copyright (c) Stuart Sierra, 2008. All rights reserved. The use
7 ;; and distribution terms for this software are covered by the Eclipse
8 ;; Public License 1.0 (http://opensource.org/licenses/eclipse-1.0.php)
9 ;; which can be found in the file epl-v10.html at the root of this
10 ;; distribution. By using this software in any fashion, you are
11 ;; agreeing to be bound by the terms of this license. You must not
12 ;; remove this notice, or any other, from this software.
13
14
15 ;; This file defines a generic "case" macro called "fcase" which takes
16 ;; the equality-testing function as an argument. It also defines a
17 ;; traditional "case" macro that tests using "=" and variants that
18 ;; test for regular expressions and class membership.
19
20
21 ;; Note (December 23, 2008): This library has been supplanted by the
22 ;; inclusion of "condp" in clojure.core as of Clojure SVN rev. 1180.
23
24
25 (ns
26 ^{:author "Stuart Sierra",
27 :doc "This file defines a generic \"case\" macro called \"fcase\" which takes
28 the equality-testing function as an argument. It also defines a
29 traditional \"case\" macro that tests using \"=\" and variants that
30 test for regular expressions and class membership.
31
32
33 Note (December 23, 2008): This library has been supplanted by the
34 inclusion of \"condp\" in clojure.core as of Clojure SVN rev. 1180."}
35
36 clojure.contrib.fcase
37 (:refer-clojure :exclude (case)))
38
39
40 (defmacro fcase
41 "Generic switch/case macro. 'fcase' is short for 'function case'.
42
43 The 'compare-fn' is a fn of two arguments.
44
45 The 'test-expr-clauses' are value-expression pairs without
46 surrounding parentheses, like in Clojure's 'cond'.
47
48 The 'case-value' is evaluated once and cached. Then, 'compare-fn'
49 is called once for each clause, with the clause's test value as its
50 first argument and 'case-value' as its second argument. If
51 'compare-fn' returns logical true, the clause's expression is
52 evaluated and returned. If 'compare-fn' returns false/nil, we go to
53 the next test value.
54
55 If 'test-expr-clauses' contains an odd number of items, the last
56 item is the default expression evaluated if no case-value matches.
57 If there is no default expression and no case-value matches, fcase
58 returns nil.
59
60 See specific forms of this macro in 'case' and 're-case'.
61
62 The test expressions in 'fcase' are always evaluated linearly, in
63 order. For a large number of case expressions it may be more
64 efficient to use a hash lookup."
65 [compare-fn case-value &
66 test-expr-clauses]
67 (let [test-val-sym (gensym "test_val")
68 test-fn-sym (gensym "test_fn")
69 cond-loop (fn this [clauses]
70 (cond
71 (>= (count clauses) 2)
72 (list 'if (list test-fn-sym (first clauses) test-val-sym)
73 (second clauses)
74 (this (rest (rest clauses))))
75 (= (count clauses) 1) (first clauses)))]
76 (list 'let [test-val-sym case-value, test-fn-sym compare-fn]
77 (cond-loop test-expr-clauses))))
78
79 (defmacro case
80 "Like cond, but test-value is compared against the value of each
81 test expression with =. If they are equal, executes the \"body\"
82 expression. Optional last expression is executed if none of the
83 test expressions match."
84 [test-value & clauses]
85 `(fcase = ~test-value ~@clauses))
86
87 (defmacro re-case
88 "Like case, but the test expressions are regular expressions, tested
89 with re-find."
90 [test-value & clauses]
91 `(fcase re-find ~test-value ~@clauses))
92
93 (defmacro instance-case
94 "Like case, but the test expressions are Java class names, tested with
95 'instance?'."
96 [test-value & clauses]
97 `(fcase instance? ~test-value ~@clauses))
98
99 (defn in-case-test [test-seq case-value]
100 (some (fn [item] (= item case-value))
101 test-seq))
102
103 (defmacro in-case
104 "Like case, but test expressions are sequences. The test expression
105 is true if any item in the sequence is equal (tested with '=') to
106 the test value."
107 [test-value & clauses]
108 `(fcase in-case-test ~test-value ~@clauses))